Mixed salt lubricants containing a controlled amount of water



United States Patent 3,152,079 D/IDTED SALT LUBRICANTS CGNTAINTNG A CONTROLLED AMOUNT OF WATER Arnold J. Morway, Clark, N.J., assignor to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Filed July 3, 1961, Ser. No. 121,365 6 Claims. (Cl. 25239) This invention relates to improvements in the preparation and composition of mixed-salt lubricating oil compositions. Particularly, the invention relates to a semifiuid lubricant comprising lubricating oil, calcium salt of acetic acid, calcium salt of C to C fatty acid and a limited amount of water.

This application is a continuation-in-part of my US. patent application, Serial No. 51,255, filed August 23, 1960, having the title Mixed-Salt Lubricants (now U.S. Patent 3,071,547), which in turn was a continuationin-part of my US. patent application, Serial No. 498,740, filed April 1, 1955 (now abandoned).

In my prior patent application, Serial No. 51,255, I have described semi-fluid lubricants comprising mineral oil and mixed calcium salts of acetic acid and C to C fatty acid, in high molar ratios of salt of acetic acid to salt of said higher fatty acid. Lubricants of this type have found wide spread commercial acceptance in the lubrication of the cylinders of marine diesel engines. These lubricants have the required extreme pressure properties, greatly reduce wear between the piston and cylinder liner of the marine diesel engine, and also successfully neutralize corrosive acids which form on these surfaces when the engine is running on a high sulfur fuel oil.

In lubricating these diesel engines, a fluid or semi-fluid lubricant is applied on the cylinder upon each stroke of the piston by means of a centralized force-feed lubrication system. The lubricant is to a large extent consumed during each stroke of the piston, thereby requiring continuous application of the lubricant. A suitable viscosity is required in order that the lubricant can be readily pumped through the aforementioned force-feed lubrication systems, and will spread or Wet the piston sufficiently during each stroke to achieve an overall coating on the piston surface. In addition, the lubricant must be storage stable.

In my prior patent application, Serial No. 51,255, it was pointed out that lubricants having the desired extreme pressure, antiwear, acid neutralizing, viscosity and storage stability properties, can be obtained by thickening oil with 5 to 12, preferably 6 to 8 wt. percent of total thickener comprising calcium salt of acetic acid or its anhydride in combination with calcium salt of C to C fatty acids, in a molar equivalent ratio of about 11.5:1 to :1 of said acetic acid or anhydride per mole equivalent of said O; to C fatty acid. It has now been found that the viscosity and storage stability of the lubricant can be improved if the lubricant contains about 0.05 to 0.10 wt. percent free water and about 0.2 to about 0.25 wt. percent total water, said wt. percent being based on a lubricant containing about 6 to 8 wt. percent of the mixed salt. If larger or smaller amounts of the mixed salt are present in the lubricant, then the amount of free water and total water can be correspondingly larger or smaller in a direct proportion.

The intermediate molecular weight acids used in preparing the mixed salt composition are those aliphatic straight chain monocarboxylic acids containing from about 7 to 10 carbon atoms. Minor amounts of a higher fatty acid such as lauric acid may also be present but the average carbon atom content of the intermediate molecular Weight acid should be within the range of 7 to 10. Either saturated or unsaturated fatty acids may be utilized, though the saturated fatty acids are preferred. The corresponding branched chain acids are not suitable since they result in unstable lubricants in which the salts readily separate from the oil. Intermediate molecular weight strai ht chain monocarboxylic acids coming within the above prescriptions are exemplified by heptanoic (en anthic), octanoic (caprylic), nonanoic (pelargonic) and decanoic (capric). Commercial mixtures of these intermediate molecular Weight carboxylic acids having an average saponification of from about 310 to 440, pref erably 320 to 420 can also be employed.

The calcium salts of the invention can be prepared by coneutralization of a mixture of the acids with suitable bases, particularly the hydroxides and/or carbonates of calcium. It is generally desirable to use a slight excess of base, e.g., lime, in order to form a slightly alkaline final product, e.g., 0.05 to 0.2 wt. percent alkalinity as measured in terms of NaOH. This alkalinity acts to neutralize corrosive acids formed by degradation of the lubricant during use and also imparts conditions of greater stability. The coneutralization step may be carried out in situ in the mineral oil menstruum to which the mixture of salts is to be applied in actual use. The maximum temperature at which coneutralization is carried out or the temperature to which the coneutralized material is heated will generally be in the range of about 250 to about 350 F. The salt mixture should be heated until the desired free water and total water content are obtained.

The free water content can be determined by mixing about 25 parts by weight of the lubricant sample with about 1 00 parts by weight of heptane as an entraim'ng agent. This mixture is then heated in a distillation flask to boiling following the general distillation procedure described in ASTM E123-56T. The heptane boils sufliciently high to remove the free, i.e., unbound, water present. The water and heptane which distill over are collected and the water layer is measured.

Total water content, which includes both free water and bound water, can be determined in a similar manner except that a higher boiling entraining agent is used in place of the heptane. For example, inert petroleum hydrocarbon solvents can be used such as Varsol #1 which is a hydrocarbon solvent having an initial B.P. of 319 F. and a final B.P. of 390 F. by ASTM D86 method. Also blends of heptane with Varsol #1, or still other solvents such as xylene, toluene, etc. can be used.

The above water tests are preferably carried out on the lubricant while dehydrating so that the dehydration can be stopped at the proper time. However, if the dehydration is carried too far, so as to result in a lubricant having insuflicient water, then additional water is added to achieve the desired water content. For example, assume that the dehydration has been carried to 0.00 wt. percent free water and 0.15 wt. percent total water (all bound water in this case). Then 0.1 wt. percent of water is 3 added to give a lubricant having 0.1 wt. percent free water and 0.25 wt. percent total water.

Various additives can be added to the finished lubricant in amount of 0.1 to 10.0 wt. percent each, based on the weight of the finished lubricant. Among additives that can be added are corrosion inhibitors such as sodium nitrite, lanolin, wool grease stearine; antioxidants such as phenyl a-naphthylamine; auxiliary extreme pressure agents; dyes; etc.

The finished lubricant will comprise a major amount of lubircating oil and about 5 to 12, preferably 6 to 8 wt. percent of the mixed salt combination. For economy purposes in heating during large scale manufacture, concentrates of 35 to 50 wt. percent of the mixed salts in oil can be made by the in situ preparation technique and then the concentrate diluted with additional oil to form the finished lubricant. This dilution is readily made by adding the additional oil and mixing in the kettle, or by using a pump around system where the lubricant is passed from the kettle to a pump and then back to the kettle until completely mixed. Both the concentrate and finished lubricant can be homogenized in a Morehouse mill, Charlotte mill, Gaulin homogenizer, etc. Where a concentrate is made, then of course, its water content can be correspondingly greater but provided that when diluted to form the final product, the final product has a water content within the previously prescribed ranges.

EXAMPLE I A grease was prepared having the following formulation:

Percent weight Naphthenic lubricating oil of 40 SUS at 210 F. 11.71 Phenol extract lubricating oil of 125 SUS at 100 F. 23.08 Phenyl a-naphthylamine 0.20

The lime and about a sixth of the 80 SUS oil, were intimately mixed, followed by the addition of about a third of the Wecoline AAC acids (a commercial mixture of coconut acids consisting of about 46 wt. percent capric, about 28 wt. percent caprylic and about 26 Wt. percent lauric acids). Then all the glacial acetic acid was added, while mixing, at a slow rate so as to keep the temperature of the reaction mass below 180 F. The remainder of the Wecoline AAC acids was then added, and the reaction mixture was thoroughly mixed and then heated to a maximum temperature of 305 F., which was held for two hours after which the heat was turned ofif and cooling begun. About a twelfth of the 80 SUS oil was added. Upon the material cooling to 220 F., the phenyl a-naphthylamine was added and all of the 40 SUS oil was added.

The product was then passed to a blending tank where the remainder of the 80 SUS oil and all the phenol extract oil was added. The product was then passed through a Cornell homogenizer and filtered through a 100 mesh Cuno Strainer. The resulting product Was analyzed and found to contain about 0.1 wt. percent total water as measured by distilling with a mixture consisting of 40 wt. percent heptane and 60 wt. percent Varsol #1. There was no free water as determined by distilling with heptane. This product was tested for 4 hours in a centrifuge operating at 1500 rpm. whereupon about 0.8 wt. percent solid precipitation occurred.

EXAMPLE II Example I repeated only the dehydration was controlled so as to obtain a final composition containing 0.2 wt. percent total water using the aforementioned heptane and Varsol #1 and a free water content of about 0.05

wt. percent using heptane. These water measurements were carried out by the ASTM E123-56T method. This Effect of Water Content on Stability and Viscosity Percent Viscosity in SUS Free Total Solid Composition Water Water Sepa- Oontent Content ration At At Example I 0.00 0. 1 8 1, 380 86 0. 01 0. 2 25 2, 550 0. 2 0. 3 15. 0 gel gel 0. 3 0. 4 17. O gel gel 0. 05 0. 2 0. 25 1, 400 87 0. 15 0. 3 25 2, 500 132 0. 25 0. 4 15. 0 gel gel 0.35 0. 5 60 0 gel gel As seen from the preceding table, the product of Example I containing only 0.1 wet. percent bound water, showed a separation of 0.8 wt. percent solid. That is, the amount of solid which precipitated during the centrifuge test was 0.8 wt. percent of the weight of the total composition. By adding 0.1 wt. percent water, which was free water, the product became more stable as noted by a solid separation of only 0.25 wt. percent while the viscosity of the product increased. Upon increasing the free water content to 0.2 wt. percent, a gel resulted and the percent solid separation drastically increased to 15%. While increasing the free water to 0.3% increased the solid separation to 17%. The high percent solid separation in these last two cases were due to the precipitation of solid gel during the centrifuge test. Example 11 shows a product having 0.05% free water and 0.2% total water having a very low solid separation, and at the same time a very low viscosity. The addition of 0.1% water maintained the same percent of solid separation but increased the viscosity. By increasing the free Water content to 0.25% and the total water content to .4%, then a gel formed, a large portion of which separated upon centrifuging. Further increasing the free water content to 0.35% resulted in an even larger separation of gel during the centrifuge test.

The preceding data of the table illustrates the necessity for maintaining the free water and the total water within the prescribed limits to obtain high stability as indicated by low percent solid separation in the centrifuge test, while at the same time avoiding gelling the lubricant.

In sum, the present invention relates to compositions containing calcium mixed salt of fatty acids having a free. water content of approximately .007 to .014 wt. percent, and a total water content of approximately .03 to .045 wt. percent, per each wt. percent of calcium mixed salt. The preferred final compositions will contain about 6 to 8 wt. percent of calcium mixed salt, will have a free water content of about 0.05 to .10 wt. percent and a total water content of 0.02 to 0.3 wt. percent, all of said weight percents being based upon the weight of the total composition. The term free water, as used herein, is unassociated water which is readily removed by distillation with heptane or a solvent having a similar boiling point, e.g., under 250 F. The term total water, as used herein, is the total of the free water and associated or bound water. This bound water is probably in the form of various hydrates and is chemically associated. By distilling with a higher boiling solvent having a boiling point of about 300 to 400 R, such as the Varsol #1, or the Varsol #1 and heptane mixture, all the water is separated from the lubricant and this constitutes the total Water.

What is claimed is:

1. A semi-fluid lubricant suitable for lubrication of upper cylinders of marine diesel engines comprising a 5 major amount of mineral lubricating oil, about 5 to 12 Wt. percent of calcium mixed salts of acetic acid and C 7 to C straight chain fatty acid in a molar ratio of said acetic acid to said fatty acid of 11.5 :1 to 25 :1, about 0.007 to 0.014 Wt. percent of free Water per wt. percent of said calcium mixed salts and about 0.03 to 0.045 wt. percent of total water per wt. percent of said calcium mixed salts.

2. A lubricant according to claim 1, wherein the amount of said mixed salt thickener is about 6 to 8 wt. percent, the amount of said free Water is about 0.05 to 0.1 wt. percent and the amount of said total water is about 0.2 to 0.3 wt. percent, all of said wt. percents being based upon weight of the total composition.

3. A semi-fluid lubricant comprising a major amount of mineral lubricating oil, about 6 to 8 Wt. percent of calcium mixed salts of acetic acid and a mixture of C to C straight chain fatty acids derived from coconut oil and averaging less than 10 carbon atoms per molecule, in a molar ratio of acetic acid to said fatty acid of about 11.5:1 to 25:1, about 0.05 to 0.1 wt. percent of free Water and about 0.2 to about 0.3 wt. percent of total water.

4. A method of preparing a semi-fluid lubricant comprising a major amount of mineral lubricating oil thickened with about 5 to 12 wt. percent of calcium mixed salt of acetic acid and C to C straight chain fatty acid averaging between 7 and 10 carbon atoms per molecule, in a molar ratio of said acetic acid to said fatty acid of 11.5 :1 to 25 :1, which comprises coneutralizing said acids in at least a portion of said oil with lime, heating to dehydrate at temperatures of about 250 to 350 F., and periodically determining the free Water content and total Water content, then stopping said dehydration when the amount of free Water is about 0.007 to 0.014 wt. percent, per wt. percent of said calcium mixed salts, and the amount of total water is about 0.03 to 0.045 wt. percent, per Wt. percent of said calcium mixed salts.

5. A method according to claim 4, wherein the free Water content is determined by heating a portion of the dehydrating lubricant with a hydrocarbon solvent having a boiling point under 250 F., distilling over a mixture of said solvent and water, recovering the distilled water, and measuring the amount of said distilled Water.

6. A method according to claim 4, wherein the total water content is determined by heating a portion of the dehydrating lubricant with a hydrocarbon solvent having a boiling range of about 300 to 400 F., and distilling over a mixture of said solvent and Water, recovering the distilled Water, and measuring the amount of said distilled water.

References Cited in the file of this patent UNITED STATES PATENTS 2,973,321 Morway et a1 Feb. 28, 1961 3,071,547 Morway Jan. 1, 1963 FOREIGN PATENTS 562,785 Great Britain July 17, 1944 OTHER REFERENCES Manufacture and Application of Lubricating Greases, by Boner, Reinhold Pub. Corp., New York, 1954, pages 37-43 and 358-362. 

1. A SEMI-FLUID LUBRICANT SUITABLE FOR LUBRICATION OF UPPER CYLINDERS OF MARINE DIESEL ENGINES COMPRISING A MAJOR AMOUNT OF MINERAL LUBRICATING OIL, ABOUT 5 TO 12 WT. PERCENT OF CALCIUM MIXED SALTS OF ACETIC ACID AND C7 TO C10 STRAIGHT CHAIN FATTY ACID IN A MOLAR RATIO OF SAID ACETIC ACID TO SAID FATTY ACID OF 11.5:1 TO 25:1, ABOUT 0.007 TO 0.014 WT. PERCENT OF FREE WATER PER WT. PERCENT OF SAID CALCIUM MIXED SALTS AND ABOUT 0.03 TO 0.045 WT. PERCENT OF TOTAL WATER PER WT. PERCENT OF SAID CALCIUM MIXED SALTS. 